1. Field of the Invention
The present invention relates generally to multicore optical fiber designs, devices, and applications.
2. Background Art
Passive optical networks (PONs) are now being deployed worldwide in large numbers for broadband access services. The rapid growth in data traffic has recently led to an exponentially growing demand for capacity in access networks. This growing demand has in turn driven an increasing need for high counts of feeder fibers, causing congestion problems in duct pipes, and like structures. Hence, low-cost, high-density cables with high fiber counts are necessary to construct practical PON systems for future optical access networks. Similar needs exist for increasing the capacity of long-haul, backbone networks, as bandwidth continues to grow unabated while technological solutions for providing such bandwidth appear to be saturating.
Multicore fiber (MCF) offers a possible solution for increasing fiber density, spectral efficiency per fiber, and for overcoming cable size limitations and duct congestion problems. The goal of multicore fiber solutions, and spatial division multiplexing in general, is to increase the bandwidth capacity of a communication link at a rate greater than the increase in cost of conventional solutions. In other words, a system which increases capacity by a factor N using spatial division multiplexing will be commercially interesting if the cost is significantly less than N times the cost of deploying conventional single-spatial-mode solutions.
Design and fabrication of several types of MCFs have been reported to address this need for high density while maintaining properties similar to those of single-core solutions, such as low loss, low crosstalk and facile connectivity. The crosstalk level, i.e. the power transferred between the cores, is determined by the refractive index profiles of the cores and surrounding cladding, as well as the core-to-core distance and the physical layout of the fiber (e.g., bends, twists, strains, and the like). The core density is dictated by the core-to-core distance and geometrical arrangement of the multiple cores. The index profile, core geometry, and coating also affect microbend and macrobend loss, as well as the nonlinear properties of the fiber. Therefore, a comprehensive design is necessary to optimize overall optical fiber parameters for MCF. Another important problem is connectivity: commercial use of MCF requires low-cost reliable splicing and coupling of signals into and out of the closely-spaced individual cores.
In addition, the demand for ever higher capacity data transmissions has attracted considerable interest in the development of high-density and high-speed parallel optical data links for a wide range of applications including interne switches, servers, future high performance computers and data centers. A low-crosstalk and low-loss fiber device that enables coupling to individual cores is important for parallel MCF transmissions.
In the case of internet switches, the increase of fiber bandwidth using DWDM technology leads to aggregate bandwidths in excess of 1 terabit per second (Tb/s). In addition, system size has increased from single-shelf to multi-rack configurations. Intrasystem, rack-to-rack interconnections can span a range of several meters to tens meters. The task of providing and managing hundreds of individual links using either copper-based or conventional fiber cables is becoming increasingly challenging.
In high performance super-computers and data centers, thousands to tens of thousands of optical links operating at 1 Gb/s up to 10 Gb/s may be present. The longest distances for multichannel parallel links in such systems are typically less than 100 m. The key requirements for ensuring successful deployment of high-density parallel optical data links in that context include low cost, high density, rapid installation, and low power consumption. The majority of work to date has focused on one-dimensional parallel optical data links, which utilize multimode fiber ribbons with a one-data-channel-per-fiber arrangement. Such fiber ribbons typically comprise a 1×12 linear array of multimode fibers on a 250 μm pitch. However, such a system configuration is costly, complicated and bulky.